One known optical resonator as described in the article "New Integrated Ring Resonator In Glass," W. J. Wang et al., Elec. Lett., Vol. 28, no. 21, page 1967-1968, Oct. 8, 1992, is a large ring resonator formed of glass that is used as a tunable wavelength selective filter for various optical frequencies. The path length of the glass resonator is on the order of 12 cm and it has a low finesse of 5. This glass ring resonator is not suitable for on-chip integration with semiconductor devices.
Another known resonator of smaller size and larger finesse is described in the article "An Optical FDM Distribution Experiment Using A High Finesse Waveguide-Type Double Ring Resonator," K. Oda et al. IEEE Photonics Tech. Lett., Vol. 6, no. 8, page 1031-1034, August 1994. The frequency division multiplexing distribution scheme of this article uses a GeO.sub.2 -doped silica double ring resonator having a diameter of 3500 .mu.m and a finesse of 200. Although the diameter of the double ring resonator is small compared to that of the glass resonator, the high bending loss in the second ring of this resonator prevents reduction in its size. Also, the second ring required to attain the relatively high free spectral range (FSR) of the device complicates the manufacturing process.